Science Objectives for EveryoneIntegrated Assessment of Long-term Cosmic Radiation Through Biological Responses of the Silkworm, Bombyx mori, in Space (RadSilk) examines the effects of radiation exposure in microgravity on silkworms.

Science Results for Everyone

Silkworm eggs are kept on the International Space Station for three months, then placed in either normal or microgravity for six days to resume embryonic development. The results show that microgravity does have an effect on egg development. Eggs are also exposed to radiation. No mutations are seen in the first generation of worms, but are present in the second and third generations, indicating that cosmic rays apparently damage the genes in the first generation and this gets passed down to later generations. Gene silencing, or deactivating, data indicate that individual eggs experienced variations in dose and type of cosmic ray, which means that researchers need to examine radiation’s effects at an individual level not the group as a whole.

The following content was provided by Toshiharu Furusawa, Ph.D., and is maintained in a database by the ISS Program Science Office.
Information provided courtesy of the Japan Aerospace and Exploration Agency (JAXA).

The eggs of the silkworm (Bombyx mori) are used as an indicator for monitoring biological responses to long-term cosmic radiation in microgravity.

Description
Eggs of silkworm Bombyx mori on the Earth in the customized egg cases. After the launch at 5 degrees C, the eggs are kept cooled in MELFI at 2 degrees C for diapause. A day before recovery STS docking, eggs are incubated using CBEF at 20 degrees C for 8 days, then stored in MELFI at +2 degrees C and -95 degrees C, then recovered at +5 degrees C and at -20 degrees C. One control egg case are kept at 2 degrees C without incubation. After recovery, eggs are germinated and analyzed for radiation effects with mutation assay, genetic assay and biochemical assays.

Earth Applications
Radiation effects are critical for biological creatures. The data collected during this investigation may lead a greater understanding of how the radiation defense system is affected by different factors from space radiation and microgravity environment. This data could potentially be used to help develop new treatments and preventative measures for radiation effects.

The environmental conditions aboard the International Space Station (ISS) include microgravity and radiation from cosmic rays and heavy ion beams. Crewmembers who stay onboard the ISS are always exposed to cosmic radiation, therefore a biodosimetric assessment of health risks associated with radiation exposure is requested. Silkworm eggs possess excellent potential to be developed into a biodosimeter. Effect of microgravity on embryonic development: Silkworm eggs that are in a dormant state (called diapause) are optimal for use on the ISS. To ensure a stable diapause state, eggs were kept at 25°C for the first 30 days after oviposition and then at 5°C for 30 days. These eggs were then transported to the ISS where they were kept continuously at 2°C for about 3 months in the incubator in the ISS until recovery. Portions of these eggs were transferred to either microgravity or 1G compartments in the Cell Biology Experimental Facility (CBEF) of the ISS, and then incubated at 20°C for 6 days to resume embryonic development. The embryos underwent development normally after exposure to microgravity and 2°C and about 50% of embryos exposed to 1G and 20°C also performed embryonic reversal. In contrast, embryos did not carry out embryonic development after exposure to microgravity and 20°C, suggesting that microgravity affects embryonic development in silkworm eggs. Chromosome aberration by cosmic rays: Heterozygous eggs exposed to heavy ion particles resulted in somatic mutations appearing as white spots on the black integument during larval stage. The white spots were caused by the loss of a chromosomal fragment carrying the PS gene from epidermal cells during growth and development. Based on the above result, the following experiments were undertaken: The Passive Dosimeter for Life Science Experiments in Space (PADLES), estimated that total cosmic radiation was 15-20mGy in the ISS over about 3 months. No mutations were seen in the integument of the larvae (first filial generation) from these eggs. However, in the second generation, the larvae exhibited white spots on the black integument of their dorsal surface, and many white spots appeared on the gray dorsal integument of p/p/PS larvae in the third generation. This indicated that cosmic rays damage genes in the primordial germ cells during embryonic development of the first generation. Effects of cosmic rays on gene expression: The cosmic radiation appeared to suppress the expression of the gene encoding a small heat shock protein among several genes known to respond to environmental stress. The extent of gene suppression in each egg was different, suggesting that the dose and type of cosmic ray that hit each egg might have varied. These results alter the focus from studying the biological effect of cosmic rays at a mass level into a more specific focus, looking at each individual level using the silkworm egg. Future research will aim to determine what type of cosmic rays and how great a dose is needed to cause chromosome aberration and suppression of gene expression.